Humans and many animals have binocular vision provided by two eyes which look in the same direction. Two parallel aligned but spaced eyes deliver two slightly different images of the same scene. This is due to the 4 to 6 cm separation between the eyes, which makes each eye have a slightly different viewpoint. The images from these two different viewpoints are sent to the brain, and this difference, which is termed parallax, is interpreted as depth. The nearer an object is to the eyes, the greater the difference between the two images. From the difference between the two images, the brain can display an impression of depth.
Stereoscopic image displays, such as stereoscopic projection for example, are based on the same principle: two slightly different images, one for the left eye and one for the right eye, are displayed by some means, e.g. projected onto a screen. A corresponding image modulating system enables the left eye to see only the left eye image, and the right eye to see only the right eye image.
In international patent application WO 2005/060270 an autostereoscopic system is described wherein for forming stereoscopic images for a plurality of users, the position of the users is taking into account. The generated stereoscopic images are generated as function of position of the user, e.g. determined with a tracking system, and images are generated such that expanded sweet spots are generated visible to various eye positions of viewers observing alternating images or a stereoscopic image sequence.
In US patent application 2004/0240777 A1 a plurality of stereoscopic imaging systems are described, wherein the system is adapted to be switchable between a two dimensional mode and an autostereoscopic three dimensional mode or to provide a multi-user display device whereby different images are displayed to different viewers.
A disadvantage of current stereoscopic imaging systems that the brightness intensity at which the images can be projected or displayed is still relatively low.